Exemple d'utilisation de services de file d'attente audio

C'est une version à l'aide de C# de la même échantillon de @lucius

    void SetupAudio ()
    {
        AudioSession.Initialize ();
        AudioSession.Category = AudioSessionCategory.MediaPlayback;

        sampleRate = AudioSession.CurrentHardwareSampleRate;
        var format = new AudioStreamBasicDescription () {
            SampleRate = sampleRate,
            Format = AudioFormatType.LinearPCM,
            FormatFlags = AudioFormatFlags.LinearPCMIsSignedInteger | AudioFormatFlags.LinearPCMIsPacked,
            BitsPerChannel = 16,
            ChannelsPerFrame = 1,
            BytesPerFrame = 2,
            BytesPerPacket = 2, 
            FramesPerPacket = 1,
        };

        var queue = new OutputAudioQueue (format);
        var bufferByteSize = (sampleRate > 16000)? 2176 : 512; //40.5 Hz : 31.25 Hz 
        var buffers = new AudioQueueBuffer* [numBuffers];
        for (int i = 0; i < numBuffers; i++){
            queue.AllocateBuffer (bufferByteSize, out buffers [i]);
            GenerateTone (buffers [i]);
            queue.EnqueueBuffer (buffers [i], null);
        }
        queue.OutputCompleted += (object sender, OutputCompletedEventArgs e) => {
            queue.EnqueueBuffer (e.UnsafeBuffer, null);
        };

        queue.Start ();
        return true;
    }

C'est le générateur de tonalité:

    void GenerateTone (AudioQueueBuffer *buffer)
{
//Make the buffer length a multiple of the wavelength for the output frequency.
uint sampleCount = buffer->AudioDataBytesCapacity / 2;
double bufferLength = sampleCount;
double wavelength = sampleRate / outputFrequency;
double repetitions = Math.Floor (bufferLength / wavelength);
if (repetitions > 0) 
sampleCount = (uint)Math.Round (wavelength * repetitions);
double      x, y;
double      sd = 1.0 / sampleRate;
double      amp = 0.9;
double      max16bit = Int16.MaxValue;
int i;
short *p = (short *) buffer->AudioData;
for (i = 0; i < sampleCount; i++) {
x = i * sd * outputFrequency;
switch (outputWaveForm) {
case WaveForm.Sine: 
y = Math.Sin (x * 2.0 * Math.PI);
break;
case WaveForm.Triangle:
x = x % 1.0;
if (x < 0.25)
y = x * 4.0; //up 0.0 to 1.0
else if (x < 0.75)
y = (1.0 - x) * 4.0 - 2.0; //down 1.0 to -1.0
else 
y = (x - 1.0) * 4.0; //up -1.0 to 0.0
break;
case WaveForm.Sawtooth:
y  = 0.8 - (x % 1.0) * 1.8;
break;
case WaveForm.Square:
y = ((x % 1.0) < 0.5)? 0.7: -0.7;
break;
default: y = 0; break;
}
p[i] = (short)(y * max16bit * amp);
}
buffer->AudioDataByteSize = sampleCount * 2;
}
}

Vous aussi vous voulez ces définitions:

    enum WaveForm {
Sine, Triangle, Sawtooth, Square
}
WaveForm outputWaveForm;
const float outputFrequency = 220;